... Now , that's all I want to say about world coal reserves . So let's move on to the next topic , renewable resources . There are three things we have to consider when talking about renewable resources . First , sustainability ; second , marketability ; lastly , the reality factor . Let's talk about each point in more detail ... John , would you like to take it from here ?   Certainly . As my colleague just mentioned , sustainability is a major concern when examining the potential output of a resource . Of course , as you can see from the content of our presentation today , with renewable resource , there is a much larger sustainability than with non-renewable resource . 